618 research outputs found
Isotope analysis of water by means of near-infrared dual-wavelength diode laser spectroscopy
A novel diode laser spectrometer was developed using dual-wavelength multiplexing, ensuring ideal conditions for high-precision and simultaneous measurements of the 2H/1H, 17O/16O, and 18O/16O isotope ratios in water. A 1.4-µm diode laser probed a H16OH/HO2H line pair near 7198 cm-1, while a similar laser observed H16OH, H17OH, and H18OH ro-vibrational lines around 7183 cm-1, or a H16OH/H18OH line pair near 7200 cm–1. The 1-σ standard deviation is 0.2‰ for 18O/16O, and 0.5‰ for the 2H/1H and 17O/16O isotope ratios. Preliminary experiments with repeated injections of a natural abundance sample point to an accuracy of about 1‰ for all three isotope ratios in natural samples.
Selected papers of the 1st International Workshop on “Stable Isotope Ratio Infrared Spectrometry:New Developments and Applications” (SIRIS), September 6–8, 2004, Vienna, Austria. Preface
Selected papers of the 1st International Workshop on “Stable Isotope Ratio Infrared Spectrometry:New Developments and Applications” (SIRIS), September 6–8, 2004, Vienna, Austria. Preface
Effect of Vadasz term on the onset of convection in a Darcy-Brinkman anisotropic rotating porous medium in LTNE
In the present paper, the effect of the Vadasz inertia term on the onset of
convective motions for a Darcy-Brinkman model is investigated. It is proved
that this term leads to the possibility for oscillatory convection to occur.
Hence, convection can occur via either oscillatory or steady motions. It is
proved analytically that the onset of steady convection is not affected by the
Vadasz term, while oscillatory convection is favoured by it. Moreover,
conditions to rule out the occurrence of oscillatory convection are determined
numerically. The influence of rotation, interaction coefficient and mechanical
and thermal anisotropies on the onset of instability is investigated, both
analytically and numerically
A Darcy-Brinkman Model for Penetrative Convection in LTNE
The aim of this paper is to investigate the onset of penetrative convection
in a Darcy-Brinkmann porous medium under the hypothesis of local therma
non-equilibrium. For the problem at stake, the strong form of the principle of
exchange of stabilities has been proved, i.e. convective motions can occur only
through a secondary stationary motion. We perform linear and nonlinear
stability analyses of the basic state motion, with particular regard to the
behaviour of the stability thresholds with respect to the relevant physical
parameters characterizing the model. The Chebyshev- method and the
shooting method are employed and implemented to solve the differential
eigenvalue problems arising from linear and nonlinear analyses to determine
critical Rayleigh numbers. Numerical simulations prove the stabilising effect
of upper bounding plane temperature, Darcy's number and the interaction
coefficient characterising the local thermal non-equilibrium regime
Observing the intrinsic linewidth of a quantum-cascade laser: beyond the Schawlow-Townes limit
A comprehensive investigation of the frequency-noise spectral density of a
free-running mid-infrared quantum-cascade laser is presented for the first
time. It provides direct evidence of the leveling of this noise down to a white
noise plateau, corresponding to an intrinsic linewidth of a few hundred Hz. The
experiment is in agreement with the most recent theory on the fundamental
mechanism of line broadening in quantum-cascade lasers, which provides a new
insight into the Schawlow-Townes formula and predicts a narrowing beyond the
limit set by the radiative lifetime of the upper level.Comment: 4 pages, 4 figure
Primary gas thermometry by means of laser-absorption spectroscopy: Determination of the Boltzmann constant
We report on a new optical implementation of primary gas thermometry based on
laser absorption spectrometry in the near infrared. The method consists in
retrieving the Doppler broadening from highly accurate observations of the line
shape of the R(12) transition in
CO gas at thermodynamic equilibrium. Doppler width measurements as a
function of gas temperature, ranging between the triple point of water and the
gallium melting point, allowed for a spectroscopic determination of the
Boltzmann constant with a relative accuracy of .Comment: Submitted to Physical Review Letter
Lamb-dip cavity ring-down spectroscopy of acetylene at 1.4 μm
Doppler-free saturated-absorption Lamb dips are observed for weak vibration-rotation transitions
of C2H2 between 7167 and 7217 cm−1, using a frequency-comb assisted cavity ring-down
spectrometer based on the use of a pair of phase-locked diode lasers.We measured the absolute
center frequency of sixteen lines belonging to the 2ν3 + ν1
5 band, targeting ortho and para states of
the molecule. Line pairs of the P and Q branches were selected so as to form a ‘V’-scheme, sharing
the lower energy level. Such a choice made it possible to determine the rotational energy
separations of the excited vibrational state for J-values from 11 to 20. Line-center frequencies are
determined with an overall uncertainty between 3 and 13 kHz. This is over three orders of
magnitude more accurate than previous experimental studies in the spectral region around the
wavelength of 1.4 μm. The retrieved energy separations provide a stringent test of the so-called
MARVEL method recently applied to acetylene
Cereal-based gluten-free food: how to riconcile nutritional and technological properties of wheat proteins with safety for celiac disease patients
The gluten-free diet is, to date, the only efficacious treatment for patients with
Celiac Disease. In recent years, the impressive rise of Celiac Disease incidence,
dramatically prompted changes in the dietary habit of an increasingly large population,
with a rise in demand of gluten-free products. The formulation of gluten-free bakery
products presents a formidable challenge to cereal technologists. As wheat gluten
contributes to the formation of a strong protein network, that confers visco-elasticity to the
dough and allows the wheat flour to be processed into a wide range of products, the
preparation of cereal-based gluten-free products is a process somehow difficult process.
This review focuses on nutritional and technological quality of products made with
gluten-free cereals available on the market. The possibility of using flour from naturally
low toxic ancient wheat species or detoxified wheat for the diet of celiacs is also discussed
Linearity of a silicon carbide photodiode in the deep-UV spectral region: implications on Doppler broadening thermometry
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